Many pourable food products, such as beverages, fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
One example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known by the trade name Tetra Brik Aseptic (registered trademark).
Another example of this type of package is the gable-top package for liquid or pourable food products, to which the following description refers purely by way of example, as described in European Patent EP1440010 and in published Patent Application EP1584563, and known by the trade name Tetra Gemina™ Aseptic.
In both cases, the package is produced by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material. More specifically, the web of packaging material is unwound off a reel and fed through an aseptic chamber on the packaging machine, where it is sterilized, e.g. by applying a sterilizing agent, such as hydrogen peroxide, which is subsequently evaporated by heating and/or by subjecting the packaging material to radiation of appropriate wavelength and intensity; and the web so sterilized is maintained in a closed, sterile environment, is folded into a cylinder, and is sealed longitudinally to form a continuous tube in known manner.
The tube of packaging material, actually forming an extension of the aseptic chamber, is fed continuously in a vertical direction, is filled with the sterilized or sterile-processed food product, and is fed through a forming unit for producing the individual packages. That is, inside the forming unit, the tube is sealed along a number of equally spaced cross sections to form a continuous strip of pillow packs connected to one another by respective transverse sealing strips, i.e. extending perpendicular to the travelling direction of the tube.
More specifically, each pillow pack comprises a parallelepiped-shaped main portion; and opposite, respectively top and bottom, end portions tapering from the main portion towards respective sealing strips. Each end portion has substantially triangular flaps projecting from opposite sides of the main portion, and a narrow rectangular tab projecting from the relative sealing strip.
The pillow packs are separated by cutting the relative transverse sealing strips, and are then folded further to form respective finished packages.
In the case of parallelepiped-shaped packages, the end portions are first flattened, and then the top flaps are folded onto respective lateral walls of the main portion, and the bottom flaps are folded onto the flattened bottom end portion.
In the case of gable-top packages, on the other hand, the top end portion of the pack is folded to form two sloping walls joined at a sealing strip, and the flaps of the bottom end portion are folded onto the flattened bottom end portion.
Within the industry, a need is felt for versatile folding units, i.e. designed to produce, quickly and with a small number of operations, packages of different heights, i.e. from pillow packs of different-sized main portions.